The present invention is directed to an improvement in a hot air heat exchanger which has a housing with a ceiling and a floor spaced from the ceiling which floor is formed by a ceiling or upper wall of an outer chamber, which contains a burner, and the heat exchanger has at least one heat exchanger pipe extending between the floor and the ceiling of the heat exchanger to carry exhuast gases from the burner.
In a hot air heat exchanger which has heat exchange pipes that extend from a floor, which is an upper wall of a chamber containing a burner for removing exhaust gases and wherein a blower may be provided, both the pipes, as well as the upper wall of the outer chamber, become extremely hot during operation. Temperatures up to 1000.degree. C. can be reached at these surfaces. As a result thereof, excessive thermal stresses will occur, particularly in the transition region between the floor of the heat exchanger housing, i.e., the upper wall of the outer chamber, and each of the heat exchange pipes. In order to guarantee a gas-tight connection between the upper wall of the chamber and each heat exchanger pipe, these are welded to one another. Apart from the fact that a welded connection makes the replacement of the components more difficult when, for example, these are corroded or become eroded by scale, it has been shown that the region of the weld ages extremely quickly during long-term operations and is, therefore, not especially durable. Since many heat exchanger pipes which have a comparatively small cross section must be employed in order to guarantee a good heat transfer from the heat exchanger pipes into the surrounding space, the problem of thermal stressing in the transition regions is greatly increased.